Portal: Prelude, as its name states it, is an unofficial prequel to the game Portal. Its story revolves around the pre-GlaDOS epoch, even before she was plugged in. At this time, test subjects were monitored by real Aperture Science employees, whose work was tedious, lengthy and repetitive. This is why they decided to build a great artificial intelligence that could both replace them in these difficult tasks, and also take responsibility for many other tasks within the complex and compete with Black Mesa's superiority.
All employees of the Aperture Science complex are now eagerly awaiting GlaDOS. Maybe even a little too eagerly, as the upcoming events will tell...
This game is totally free. It offers a bit more gameplay hours than the original Portal, with 8 chapters, 19 test chambers, 48 challenges, 6 advanced maps, a brand new storyline and more than 400 lines of english speech with dozens of subtitles translations.

Amazing game. The puzzle where really challanging! Really fun gameplay and very nice modeling/reskining. The only problems I found with the mod was that it could use better lipsyncing and voice acting. Sounds like everyone is bored. Even during the chaos GLaDOS is causing. Other then that. Awesome mod!

It must be admitted that if you take nothing else from this mod, its sheer scale is quite exceptional. With new characters, voicework, puzzles and approximately double the length of the original portal (not to mention its difficulty in places) it is hard to den the dedication and hard work that has gone into this mod. The storyline is fairly solid – although I expected the malice of on of the observers to continue – which is impressive and a testament to what can happen if a mod team sit down…